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Have You Heard? Are cats taking an unhealthy bite out of wildlife? (Transcript)

Mar 01, 2013

By dvm360.com staff

VETERINARY MEDICINE

GETTY IMAGSE / JOEY WAITSCHAT

Stirring controversy, an investigation into the impact cats have on wildlife in the United States aims to put some numbers to the predatory nature of domestic free-ranging cats. Researchers from the Smithsonian Conservation Biology Institute's Migratory Bird Center and the U.S. Fish and Wildlife Service's Division of Migratory Birds searched existing research to identify studies that document cat predation on birds and mammals. A systematic review and quantitative estimate of mortality caused by cats was undertaken with the results further analyzed based on owned and un-owned cat populations.

The design

Owned cats were defined as those spending at least some time indoors but also given outdoor access. Unowned cats consisted of truly feral cats; any cats that did not go indoors, such as barn or farm cats; and strays that were fed by people. Also in this group were trap-neuter-return colonies.

Seeking the most reliable data, the researchers included studies incorporating cat owners' daily records of prey returns but not those that simply included an estimate. Data used to determine predation rates also came from stomach and scat contents, and separate values for birds and mammals were calculated. Predation rate was then either extracted from the studies or calculated based on the data. Only average estimates of mortality were used, excluding high estimates when provided.

The results

The results of this study reveal that an estimated 1.4 to 3.7 billion birds and 6.9 to 20.7 billion mammals—cats' preferred prey—are killed by domestic cats annually. Not surprisingly, unowned cats are responsible for most of these numbers, but the impact of owned cats is also significant. These findings exceed all previous estimations and put cat predation above every other cause of mortality in these species, such as collisions with vehicles or windows and habitat destruction. Reptiles and amphibian populations are likely also impacted heavily, and the researchers suggest that further research should be undertaken to identify predation rates for these taxa as well.

The controversy

Why is this study a concern for some cat advocates? Worries exist that the study's findings are being inaccurately reported and its estimates of cat predation will discourage cat adoption and encourage large-scale extermination of feral cats. And while most concur that cats are best kept indoors for their own health and safety, some strongly believe that cats deserve a bit of outdoor time. Additionally, many animal welfare organizations promote cat trap-neuter-return programs and think that the impact of cat predation presented in this study is inflated. Based on the findings of another research study,1 these researchers note that trap-neuter-return colonies are ineffective in reducing feral cat populations and consequently do not protect wildlife from cat predation.

Despite these differences, few argue that the impact of cat predation on wildlife is great. These wildlife mortality estimates emphasize the criticality of this problem and bolster the need for further science-based discussion on what constitutes responsible cat ownership and management of feral cat populations, as well as on the best approach to wildlife conservation.